In view of the resistance to the continued use of chlorofluorocarbons (CFCs) as propellants in so-called aerosols (pressurized containers for dispensing and atomising liquids), other propellants have had to be considered. Low boiling point gases such as propane, butane and dimethylether have been used, but have other disadvantages which render them undesirable for this particular purpose.
The advantage of using a low boiling point gas (which is in liquid form at normal ambient temperatures), is that a constant pressure within the container is maintained while any of the liquid gas remains in the container, so ensuring a relatively constant propellant pressure source throughout the whole of the discharge life of the container. This advantage is not realized if a permanent gas such as nitrogen is used as the propellant. If such a gas is used, the propellant pressure drops during the discharge due to the increasing volume which it must occupy as the liquid is to be discharged from the container. Since the temperature remains approximately constant, the decrease in pressure is substantially proportional to the increase in volume within the container. The reducing pressure results in a change in spray characteristics such a spray angle, droplet size and distribution.
A number of regulators have been proposed to provide constant mass flow rate by compensating for the falling pressure, but most have involved moving parts such as spring loaded pistons which increase costs and decrease reliability; and it is an object of the present invention to provide a regulator or discharge valve, and a method of so regulating flow, which will produce a substantially constant spray characteristic over a considerable range of propellant pressure.